1. Field of the Invention
The present invention relates to a printing apparatus, and a method for manufacturing a print substrate, an electron source and an image displaying device using such a printing apparatus, and more particularly, it relates to a print substrate, an electron source and an image displaying device using such a printing apparatus, in which poor printing can be prevented when the print substrate such as a color filter and the electron source of the image displaying device are manufactured by printing.
2. Related Background Art
Recently, as image displaying devices for substituting for bulky and heavy Braun tubes, thin flat plate-shaped image displaying devices have been used. Among the flat plate-shaped image displaying devices, although liquid crystal displaying devices have been investigated and developed vigorously, the liquid crystal displaying device still has disadvantages in that an image becomes dark and that an angle of view is narrow. Further, as displays for substituting for the liquid crystal displaying devices, displays of self light emitting type, i.e., plasma displays, and displays using electron emitting elements such as fluorescent display tubes or surface conduction type electron emitting elements have been proposed. In the display of the self light emitting type, a brighter image can be obtained and the angle of view is wider, in comparison with the liquid crystal displaying device. On the other hand, recently, a Braun tube including a picture plane displaying portion having a dimension of 30 inches or more has been proposed, and larger Braun tubes have been requested. However, when the Braun tube is made large-sized, an installation space increases accordingly.
A flat plate-shaped display of self light emitting type is suitable for a large and bright display. The inventors paid attention to image displaying devices using electron emitting elements (among the flat plate-shaped image displaying devices of self light emitting type), particularly, an image displaying device using a surface conduction type electron emitting element proposed by M. I. Elinson et al. (Radio Engineering and Electronic Physics, No. 10, pp. 1290-1296, (1965)), in which emission of electrons could be achieved with a simple arrangement.
In the surface conduction type electron emitting element, electrons are emitted by flowing current through a thin film having a small area formed on a substrate in parallel with a surface of the film. As such surface conduction type electron emitting elements, a type using SnO2 film proposed by M. I. Elinson et al., a type using Au film proposed by G. Dittmer (Thin Solid Films, No. 9, pp. 317-320 (1972)), a type using In2O3/SnO2 film proposed by M. Hartwell and C. G. Fonstad (International Electron Devices Meeting Technical Digest, pp. 519-521 (1975)) and a type using carbon film proposed by Hisashi Araki et al. (Journal of the Vacuum Society of Japan, Vol. 26, page 22 (1983)) have been disclosed.
FIG. 10 is a schematic view showing an element structure proposed by M. Hartwell as a typical example of the surface conduction type electron emitting element. In FIG. 10, the reference numeral 1001 denotes a substrate. A conductive thin film 1004 consists of metal oxide film formed by spattering in an H-shaped pattern, and an electron emitting portion 1005 is formed by communication treatment called communication forming (described later). Incidentally, in FIG. 10, a distance L between element electrodes 1002, 1003 is selected, for example, to be 0.5 to 1 mm and a width Wxe2x80x2 is selected to be about 1 mm.
U. S. Pat. No. 5,066,883 discloses a surface conduction type electron emitting element in which fine particles for emitting electrons are dispersed and disposed between a pair of element electrodes. This electron emitting element can control an electron emitting position, in comparison with the abovementioned conventional surface conduction type electron emitting elements.
FIGS. 11A and 11B show typical element structures of this surface conduction type electron emitting element. FIG. 11A is a plan view of the element structure and FIG. 11B is a sectional view of the element structure. In FIGS. 11A and 11B, the reference numeral 1101 denotes an insulation substrate; 1102, 1103 denote element electrodes for achieving electrical connection; and 1104 denotes a conductive thin film. In this surface conduction type electron emitting element, a distance L between the pair of element electrodes is selected to be 0.01 to 100 xcexcm, and a gap 1105 is formed in the conductive thin film 1104. Further, it is desirable that each element electrode has a thickness d of 200 nm or less in order to achieve electrical connection to the conductive thin film.
The inventors have investigated maximizing an area of an image displaying device in which a plurality of such surface conduction type electron emitting elements are disposed on the substrate. Various methods for manufacturing an electron source substrate in which the electron emitting elements and wirings are disposed on the substrate were considered, and, among them is a method for forming element electrodes and parallel wires by photolithography.
On the other hand, a method for forming an electron source substrate including such a surface conduction type electron emitting element by using a printing technique such as screen printing, offset printing or the like was also considered.
The printing method is suitable for forming a pattern having a large area. A number of surface conduction type electron emitting elements can be formed on the substrate by manufacturing the element electrodes of the surface conduction type electron emitting element by the printing method. Further, the manufacturing cost can be reduced. In the formation of the element electrode by using the printing method, the offset printing technique suitable for forming the thin film is advantageous. An example of the offset printing technique being applied to formation of a circuit substrate is disclosed in Japanese Pat. Application Laid-open No. 4-290295.
According to the substrate disclosed in the above Japanese patent document, in order to eliminate poor coupling due to dispersion in dimension of electrode pitches caused by expansion/contraction of the pattern during the printing, angles of a plurality of coupling electrodes to be connected to parts of the circuit are changed. Further, in the above Japanese patent application, a technique in which the electrode pattern is formed by the offset printing is described.
Generally, in the offset printing, after ink is loaded on an intaglio having a desired pattern, a rotating barrel called a blanket contacts the intaglio so that the blanket receives the ink. Thereafter, the rotating blanket contacts a glass substrate, thereby transferring the desired ink pattern onto a surface of the glass substrate.
In this way, in consideration of movement of the ink, one printing cycle is completed by three main stages, i.e., the loading step, receiving step and transferring step.
The printing ink can appropriately be selected on the basis of a function of the pattern to be formed. That is to say, regarding an electrode pattern for a recording thermal head and the like, ink mainly including organic Au metal called an Au resinated paste is used, and, regarding a color filter used in a liquid crystal displaying device, ink in which R (red), G (green) and B (blue) pigments are dispersed or ink including organic coloring matter is used. The solvent for such inks may be an organic solvent such as terpineol or butyl Carbitol.
When the organic solvent is used as the ink solvent in this way, as the ink pattern is transferred from the blanket to the glass substrate, the ink solvent penetrates into the blanket (mainly cylindrical rubber) to enhance a cohesive force of ink and to reduce interfacial tension between the ink pattern and the blanket, with the result that the ink is apt to be transferred to the glass substrate. This fact is described in Japanese Pat. Application Laid-open No. 7-156523.
In this case, when a medium to be printed has absorbing power such as paper, the ink solvent in the blanket also penetrates into the medium to be printed to some extent, thereby preventing excessive expansion of the blanket.
However, when the medium to be printed has no absorbing power such as glass, the ink solvent gradually accumulates in the blanket to increase the density of the ink solvent. If the amount of ink solvent exceeds a certain predetermined value, poor transferring will occur or the blanket will be expanded by the solvent, with the result that dimensional accuracy required for prints cannot be obtained, thereby causing poor printing.
In order to prevent inconvenience caused when the blanket absorbs excessive ink solvent, in some cases, the printing process is stopped temporarily, and hot gas is blown on the blanket to vaporize or dry the organic solvent absorbed in the blanket, and the printing process is restarted after cooling. However, if the continuous printing process is temporarily stopped and the blanket treatment operation is performed, productivity will be worsened.
On the other hand, if the density of ink solvent in the blanket is too low, the solvent in the received ink pattern is excessively absorbed in the blanket rubber and is solidified on the blanket surface, with the result that, even when the blanket is closely contacted with the glass substrate to transfer the ink pattern to the glass plate, the ink pattern may still remain on the blanket surface, thereby causing poor printing. In such a case, as described in Japanese Patent Application Laid-open No. 8-48070, it is required that ink solvent be previously penetrated into the silicone rubber of the blanket in any manner before initiation of the printing.
If the poor print generated by improper amount of ink solvent in the blanket is obtained when using a cheap and disposable medium such as paper, the poor print may be discarded as it is.
However, when the print is obtained when using an electrode, wiring and/or color filter of an image displaying device, since various structures were already formed before the offset printing or since the cost of the medium to be printed itself, such as special glass, is high, the poor print cannot be discarded freely. Further, if regeneration or reuse is achieved in any way, cost will be increased.
In the past, since countermeasures were considered in the stage where the poor printing was generated due to excessive expansion or excessive drying of the blanket, poor prints were eventually generated. Further, since all portions (several hundred-thousand points) of an ultra-fine pattern had to be checked to find the poor print, throughput was worsened and the total cost was increased.
An object of the present invention is to provide a printing apparatus capable of minimizing occurrence of poor print.
Another object of the present invention is to provide a method for manufacturing a print substrate, in which parts of a desired pattern can be formed on a substrate in a reproducible manner
A further object of the present invention is to provide a method for manufacturing an electron source, in which a plurality of electron emitting elements can be formed on a substrate in a reproducible manner.
A still further object of the present invention is to provide a method for manufacturing an image displaying device, in which an image displaying device capable of displaying an image with high quality can be manufactured in a reproducible manner.
Still another object of the present invention is to provide a method for manufacturing a print substrate, an electron source or an image displaying device, in which throughput can be improved considerably.
The present invention provides an offset printing apparatus for transferring an ink pattern onto a medium to be printed through a blanket, comprising a detecting means for detecting an amount of ink solvent penetrated into the blanket.
The detecting means may be a means for detecting light reflected from the blanket or a means for measuring a thickness of the blanket.
The present invention may further comprise a control means for controlling the amount of ink solvent penetrated into the blanket.
The control means may be a means for maintaining the amount of ink solvent penetrated into the blanket within a desired range.
Further, the present invention provides a method for manufacturing a print substrate, wherein parts of a desired pattern are formed on a substrate by using the above-mentioned printing apparatus.
In this method, conductive members may be formed as the desired pattern.
The present invention further provides a method for manufacturing an electron source including a plurality of electron emitting elements and wirings for interconnecting the plurality of electron emitting elements on a substrate, wherein the plurality of electron emitting elements are manufactured by using the above-mentioned printing apparatus.
In the electron source manufacturing method, the electron emitting element may comprise a pair of electrodes, and a conductive thin film having an electron emitting portion disposed between the pair of electrodes, and the pair of electrodes may be manufactured by using the above-mentioned printing apparatus.
In the electron source manufacturing method, wiring for the electron source may be formed by using a screen printing method.
Further, the present invention provides a method for manufacturing an image displaying device comprising an electron source including a plurality of electron emitting elements and wirings for interconnecting the plurality of electron emitting elements, and a fluorescent body lighted by electrons emitted from the electron source on a substrate, wherein the electron source is manufactured by the above-mentioned method.